JP2010287682A - Back protective sheet for solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back protective sheet for a solar cell module that has shape change (shrinkage) suppressed in a laminating step of a module fabricating process while having weatherability, insulation, etc., of high level. <P>SOLUTION: The single-layer or multilayer back protective sheet for the solar cell module includes at least one layer of a weather-resisting resin sheet (A) containing ultra-high molecular weight polyethylene of ≥5 dl/g in intrinsic viscosity. The weather-resisting resin sheet (A) has no or plus thermal expansion (both in an MD direction and in a TD direction perpendicular thereto) when heated at 30 to 120°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sheet for protecting the back surface of a solar cell module.

  A solar cell module generally has a front substrate, a resin-encapsulated solar cell, and a back surface protection sheet. The solar cells convert the solar energy incident through the front substrate or the back protective sheet into electricity.

  In general, the back surface protection sheet of the solar cell module is required to have weather resistance, moisture resistance, insulation, and the like. Therefore, back surface protection sheets of various materials have been proposed. In addition, it has been proposed that the back surface protection sheet is a laminated sheet including a weather-resistant resin sheet and a moisture-proof sheet.

  For example, it is known that a laminated sheet of a sheet made of polyvinyl fluoride (PVF) and a sheet made of polyethylene terephthalate is used as a back surface protection sheet for a solar cell module (see Patent Document 1). It can be considered that PVF exhibits weather resistance and polyethylene terephthalate exhibits moisture resistance.

  Also, a laminated sheet of a sheet made of relatively high density polyethylene and a sheet made of polyethylene terephthalate (see Patent Document 2), a sheet made of linear low density polyethylene, polyvinylidene fluoride and polymethyl methacrylate It has also been proposed to use a laminated sheet (see Patent Document 3) with the contained sheet as a back surface protection sheet for a solar cell module.

  On the other hand, in a laminate of a weather-resistant resin film, a highly moisture-proof film, and an adhesive resin layer, a back surface protection sheet for a solar cell module using ultrahigh molecular weight polyethylene as a highly moisture-proof film is known (for example, a patent (Ref. 4).

JP-T 8-500214 JP-A-11-261085 JP 2008-211034 A JP 62-40783 A

  As above-mentioned, a weather resistance, insulation, etc. are calculated | required by the back surface protection sheet of a solar cell module. On the other hand, the manufacturing process of the solar cell module includes a step of laminating and laminating a module constituent member (including a front surface substrate, a battery cell, a sealing film, and the like) and a back surface protective sheet. Since this lamination is performed under a high temperature condition, the shape of the back surface protection sheet changes, for example, shrinks, and thus wrinkles occur, and an appropriate solar cell module may not be obtained. Thus, there has been a demand for a protective sheet having a high degree of weather resistance and the like, in which shape change (shrinkage) in the laminating process is suppressed.

  The present inventor has paid attention to the fact that ultrahigh molecular weight polyethylene satisfies characteristics (such as weather resistance and insulation properties) required for the back surface protection sheet of the solar cell module. However, it was found that the ultrahigh molecular weight polyethylene sheet contracted by heating, and the present invention was found by examining the suppression of the contraction.

That is, the 1st of this invention is related with the back surface protection sheet for solar cell modules shown below.
[1] A back protective sheet for a solar cell module having a single layer or a laminate, comprising at least one weather resistant resin sheet (A) containing an ultrahigh molecular weight polyethylene having an intrinsic viscosity of 5 dl / g or more,
The back surface protection sheet for solar cell modules whose thermal expansion in 120 degreeC (both thermal expansion in MD direction and thermal expansion of TD direction perpendicular | vertical to it) of the said weather resistant resin sheet (A) is zero or positive.
[2] The back surface protective sheet for a solar cell module according to [1], wherein the weather resistant resin sheet (A) is an ultrahigh molecular weight polyethylene sheet formed by cutting.
[3] The back surface protective sheet for solar cell modules according to [1] or [2], wherein a moisture proof sheet (B) is further laminated.
[4] The back protective sheet for a solar cell module according to [3], wherein the moisture-proof sheet (B) is a metal aluminum sheet or a resin sheet having an inorganic film.
[5] The back surface protective sheet for solar cell module according to any one of [1] to [4], wherein the surface of the weather resistant resin sheet (A) is subjected to corona treatment or atmospheric pressure plasma treatment.

2nd of this invention is related with the solar cell module and power generation equipment shown below.
[6] A solar cell module having a laminated back surface protection sheet,
The solar cell module whose said back surface protection sheet is a back surface protection sheet for solar cell modules in any one of [1]-[5].
[7] A power generation facility comprising the solar cell module according to [6].

  The protective sheet of the present invention has a high level of weather resistance and insulating properties normally required for a back surface protective sheet of a solar cell module, and is less prone to wrinkles in the laminating step in the module manufacturing process. Therefore, the manufacturing process of the solar cell module is facilitated.

It is a figure which shows the structural example of a solar cell module.

  The back surface protection sheet for the solar cell module of the present invention includes a weather resistant resin sheet containing ultra high molecular weight polyethylene; and may further include a moisture proof sheet laminated on the weather resistant resin sheet.

About the weather resistant resin sheet The weather resistant resin sheet includes ultra high molecular weight polyethylene. Ultra high molecular weight polyethylene is polyethylene having a molecular weight of 1 to 7 million. Ultra high molecular weight polyethylene is generally said to have low water absorption and excellent dimensional stability. The intrinsic viscosity of the ultrahigh molecular weight polyethylene contained in the protective sheet of the present invention is preferably 5 dl / g or more, and more preferably 20 dl / g or more. Intrinsic viscosity is measured in decalin at 135 ° C. Intrinsic viscosity can be adjusted by molecular weight.

  The ultra high molecular weight polyethylene may be a homopolymer of ethylene; however, it may be a copolymer with other monomers. For example, a graft copolymer of ethylene and maleic anhydride can have high adhesion to EVA (ethylene vinyl acetate copolymer), which is commonly used as a sealing resin for solar cell modules.

  Since ultrahigh molecular weight polyethylene has low fluidity, a sheet is produced by an inflation method or a grinding process called skive. In general, the inflation method is a cheaper processing method, but because it is stretched strongly, when it is laminated at a high temperature of 150 ° C. in modularization, there is a problem that wrinkles are generated due to shrinkage. On the other hand, if the sheet is made by skive, wrinkles do not occur even at high temperature lamination. That is, it has been found that even the same resin may not be applied as a back surface protection sheet depending on the sheeting process. Specifically, if the thermal expansion when the sheet is heated to 120 ° C. is 0 or positive, wrinkles will not occur, and if it is negative, wrinkles will occur. The thermal expansion of the ultra-high molecular weight polyethylene sheet obtained by cutting becomes 0 or positive, and expands without contracting when heated.

  In order to produce an ultrahigh molecular weight polyethylene sheet by cutting (skive), the sheet may be obtained by cutting from a cylindrical ultrahigh molecular weight polyethylene block produced by sintering molding with a device similar to a lathe.

  The thickness of the weather resistant resin sheet containing ultrahigh molecular weight polyethylene is preferably 0.01 mm to 1 mm, and more preferably 0.02 mm to 0.2 mm. This is because sufficient weather resistance is obtained, and lamination to the solar cell module is easy.

  The weather resistant resin sheet containing ultra high molecular weight polyethylene is characterized in that the thermal expansion when heated is 0 or positive. Specifically, the thermal expansion when heated from 30 ° C. to 120 ° C. is preferably 0 or positive. Further, the thermal expansion of the sheet is preferably 0 or positive in both the longitudinal thermal expansion and the lateral thermal expansion of the sheet. The positive thermal expansion when heated means that it expands when heated and does not shrink.

  As will be described later, the protective sheet of the present invention is laminated with other members to become a constituent member of the solar cell module. The temperature of this laminate is often about 120 ° C. In the laminate, if the protective sheet shrinks, wrinkles are generated, which is not preferable. Therefore, the occurrence of wrinkles is prevented by setting the thermal expansion of the weather resistant resin sheet included in the protective sheet to 0 or positive.

  The thermal expansion may be 0 or positive, but its absolute value is preferably small. For example, the coefficient of thermal expansion when heated from 30 ° C. to 120 ° C. may be 0 or positive. The coefficient of thermal expansion can be determined by TMA (thermomechanical analyzer). The measurement sample may be 20 mm long × 4 mm wide, heated at 10 ° C./min, and measured with a load of 5 g.

  In order to make the thermal expansion of the weather resistant resin sheet containing ultra high molecular weight polyethylene 0 or positive and to reduce the absolute value thereof, as described above, ultra high molecular weight polyethylene prepared by cutting is used, or in advance What is necessary is just to control by annealing to 150 degreeC or more.

  The weather resistant resin sheet containing ultrahigh molecular weight polyethylene may contain any additive. Examples of the additive include various fillers, ultraviolet shielding agents, ultraviolet absorbers, antioxidants and the like. Examples of the filler include talc, mica, calcium carbonate, sericite, graphite, aluminum hydroxide, iron oxide and the like. Examples of the ultraviolet shielding agent include titanium oxide, zinc oxide, carbon black and the like. Examples of the ultraviolet absorber include benzophenone derivatives, salicylic acid esters, benzotriazole derivatives, piperidine derivatives, benzoate derivatives, tin organic compounds, thiazolidone and the like. Examples of the antioxidant include phenol derivatives, allylamine derivatives, phosphites and the like.

  The protective sheet of the present invention may contain one or two or more weather resistant resin sheets. For example, a weather-resistant resin sheet may be laminated on both surfaces of a moisture-proof sheet described later.

About a moisture-proof sheet The protection sheet of this invention may have a moisture-proof sheet as above-mentioned. Examples of the moisture-proof sheet include an aluminum sheet or a resin sheet having an inorganic film. The thickness of the aluminum sheet that is a moisture-proof sheet is preferably 20 μm or more. Examples of the resin sheet having an inorganic film include a sheet (film) in which an inorganic film is formed by vapor deposition of silica, alumina or the like on PET.

  When a moisture-proof sheet is included in the protective sheet of the present invention, it is preferable to laminate a weather-resistant resin sheet containing ultrahigh molecular weight polyethylene and a moisture-proof sheet. A weather-resistant resin sheet may be laminated on one or both sides of the moisture-proof sheet; a moisture-proof sheet may be laminated on both sides of the weather-resistant resin sheet. Generally, a weather resistant resin sheet is laminated on both sides of a moisture-proof sheet. Lamination of the weather-resistant resin sheet and the moisture-proof sheet may be performed via an adhesive, may be performed by a laminating method or a pressing method, or may be coextruded.

  In order to improve the adhesion between the weather resistant resin sheet containing ultrahigh molecular weight polyethylene and the moisture proof sheet, the surface of the weather resistant resin sheet (at least the surface on which the moisture proof sheet is laminated) is subjected to a surface treatment. Is preferred. Examples of the surface treatment include corona treatment and atmospheric pressure plasma treatment. In particular, atmospheric pressure plasma treatment is preferable. Specific examples of conditions for atmospheric pressure plasma treatment include treatment using argon gas.

About solar cell module The protective sheet of this invention is used as a back surface protection sheet for solar cell modules. The form of the solar cell module may be silicon-based (crystal silicon-based or amorphous silicon-based), compound-based or organic-based; thin-film type or tandem type; super straight type (transparent Any type of solar light entering through a front surface substrate) or a substrate type (in which solar light enters through a transparent back surface protective sheet disposed opposite to the front surface substrate); May be. However, since the protective sheet of the present invention is not necessarily transparent, it can be usually applied to a super straight type solar cell module.

  A configuration example of the solar cell module is shown in FIG. The solar cell module 1 can be manufactured by laminating the front substrate 10, the sealing sheet 15, the silicon battery cell 12, the sealing sheet 15 ′, and the back surface protection sheet 11. Silicon battery cell 12 includes silicon 13 connected in series by wiring 14. The sealing sheets 15 and 15 'are an ethylene vinyl acetate copolymer usually referred to as EVA. The protective sheet of the present invention can be used as the back surface protective sheet 11.

  As described above, the production of the solar cell module includes a laminating process. The lamination temperature is usually about 150 ° C., and the weather resistant resin sheet included in the protective sheet of the present invention has zero or positive thermal expansion when heated from 30 ° C. to 120 ° C. (Swells), so there is no wrinkle when laminating. On the other hand, a sheet having a negative thermal expansion (shrinks) when heated to a high temperature generates wrinkles when laminated. As described above, in order to set the thermal expansion of the protective sheet of the present invention to 0 or more, it is preferable to use an ultra high molecular weight polyethylene sheet produced by a skive method. The laminating temperature of 150 ° C. is a temperature equal to or higher than the melting point of the ultrahigh molecular weight polyethylene, but the weather resistant resin sheet of the present invention does not shrink beyond the melting point and the resin does not flow.

  Durability is required for the back surface protection sheet for solar cell modules. The durability includes weather resistance, hydrolysis resistance, wear resistance, and the like. Moreover, electrical insulation is calculated | required by the back surface protection sheet for solar cell modules. Since ultra-high molecular weight polyethylene has both high durability and insulation, the protective sheet of the present invention is suitable as a back protective sheet for solar cell modules.

  Further, sunlight enters a super straight type solar ionization module through a transparent surface substrate (glass substrate or the like), and the silicon battery cell generates power. The back protective sheet is also required to have a function of increasing the utilization factor of sunlight by reflecting sunlight incident from the transparent substrate. Therefore, if an aluminum sheet is used as the moisture-proof sheet, the reflectance of sunlight is improved and the utilization factor of sunlight is increased.

[Example 1]
Ultra high molecular weight polyethylene (Hi-Zex Million, Mitsui Chemicals) was cut (skive method) to produce a 150 μm thick sheet, and processed by an inflation method to produce a 50 μm thick sheet.

  The thermal expansion coefficient of the obtained ultra high molecular weight polyethylene sheet was measured by TMA. The expansion coefficient in 30 degreeC-120 degreeC was calculated | required about each of TD direction perpendicular | vertical with respect to MD direction and MD direction of a sheet | seat.

  The ultrahigh molecular weight polyethylene sheet obtained by the skive method was expanded by heating, and the thermal expansion coefficient was + 2.7 / + 6.2 times (MD / TD). On the other hand, the ultrahigh molecular weight polyethylene sheet obtained by the inflation method was shrunk by heating, and the coefficient of thermal expansion was -1.0 / -0.1 times (MD / TD).

  An adhesive (Takelac / Takenate, Mitsui Chemicals) was applied to both sides of an aluminum foil (20 μm) so that the thickness after curing was about 3 μm, and the ultrahigh molecular weight polyethylene sheet obtained above was laminated. After curing at room temperature for 1 day, a protective sheet was obtained by annealing at 40 ° C. for 50 hours to crosslink the adhesive.

  The obtained protective sheet was laminated on an ethylene vinyl acetate copolymer sheet (Solar Eva (registered trademark) SC50T, thickness 450 μm, Mitsui Chemicals Fabro Co., Ltd.). Lamination conditions were 150 ° C. for 15 minutes, 140 ° C. for 15 minutes, or 130 ° C. for 15 minutes.

  As shown in Table 1, the protective sheet having a UHPE (ultra high molecular weight polyethylene) sheet produced by the skive method was not shrunk and wrinkled when laminated on the EVA sheet. On the other hand, the protective sheet containing the UHPE sheet produced by the inflation method contracted when laminated on the EVA sheet, and wrinkled when the lamination condition was 150 ° C. The shrinkage rate was determined by measuring the dimensions before and after lamination.

[Example 2]
The ultrahigh molecular weight polyethylene sheet obtained by the same method as the skive method described above is subjected to corona treatment; atmospheric pressure plasma treatment (treatment conditions: Ar flow rate: 20 L / min, voltage: 40 V, frequency: 30 kHz, treatment speed; 0.2 m / min) was applied; or an untreated surface was prepared. Lamination was carried out on both sides of an aluminum foil (20 μm) with the surface treated surface of each ultra-high molecular weight polyethylene sheet facing (the laminated structure was polyethylene sheet / aluminum foil / polyethylene sheet). The aluminum foil and the ultra high molecular weight polyethylene sheet were bonded via an adhesive (Takelac / Takenate).

The measurement results of the peel strength between the aluminum foil and the ultrahigh molecular weight polyethylene sheet are shown below.
No surface treatment: 0 N / cm (no contact)
Corona treatment: 8.2 to 8.3 N / cm
Atmospheric pressure plasma treatment: 9.2 to 10.3 N / cm

  As described above, the ultra high molecular weight polyethylene sheet not subjected to the surface treatment could not obtain sufficient adhesion with the aluminum foil, but the ultra high molecular weight polyethylene sheet subjected to the corona treatment or the atmospheric pressure plasma treatment was used. And had adhesion to aluminum foil.

[Example 3]
The ultrahigh molecular weight polyethylene sheet (50 μm) obtained by the skive method was laminated on an aluminum foil (25 μm) to obtain a protective sheet. The obtained protective sheet was evaluated for weather resistance, hydrolysis resistance, and insulation under the following conditions. The results are shown in Table 2.

A weather resistance test (test time: 1000 hours, backing plate temperature: 83 ° C., rain: none) was performed with a sunshine weather meter (based on JIS A1415), and the degree of deterioration was visually observed to evaluate the weather resistance.
Evaluation criteria:
○ Almost no discoloration and no peeling or cracking.
Δ: Some discoloration occurred, but no peeling or cracking occurred.
X Significant discoloration occurred or peeling or cracking occurred.

The protective sheet was stored under high temperature and high humidity at 85 ° C. and 85% RH × 3000 hours, and the degree of deterioration of the appearance was visually observed to evaluate hydrolysis resistance.
Evaluation criteria:
○ Almost no discoloration and no peeling or cracking.
Δ: Some discoloration occurred, but no peeling or cracking occurred.
X Significant discoloration occurred or peeling or cracking occurred.

After the protective sheet was stored under high temperature and high humidity at 85 ° C. and 85% RH × 3000 hours, the dielectric breakdown voltage was determined by a method based on JISC2151, and the insulation was evaluated.
Evaluation criteria:
○ 20kV / mm or more △ 10-20kV / mm
× Less than 10 kV / mm

  Instead of the ultrahigh molecular weight polyethylene sheet, in Comparative Example 1, a PVF sheet (Tedlar (registered trademark), thickness 50 μm, DuPont) was used; in Comparative Example 2, a PEN sheet (Teonex (registered trademark), thickness 50 μm, Teijin) In Comparative Example 3, a low oligomer PET sheet (Lumirror X10S (registered trademark), thickness 50 μm, Toray Industries, Inc.); In Comparative Example 4, a liquid crystal polymer sheet (Bexter (registered trademark), thickness 50 μm In Comparative Example 5, an HDPE sheet (Tamapoly HD, thickness 50 μm, Tamapoli Co., Ltd.) was used; in Comparative Example 6, an LLDPE sheet (Tosero TUX-HC, thickness 50 μm, Tosero Co., Ltd.) was used. A protective sheet was obtained.

  The obtained protective sheet was evaluated for weather resistance, hydrolysis resistance, and insulation. The results are shown in Table 2.

  As shown in Table 2, the protective sheet containing the ultrahigh molecular weight polyethylene (Example) had good evaluation items. As shown in the comparative example, the protective sheet including another resin sheet is in any evaluation item. Moreover, PVF widely used as a back surface protection sheet for solar cell modules is also expensive.

  The back surface protection sheet for solar cell modules of the present invention has high durability and insulation required for the back surface protection sheet, and does not shrink and does not generate wrinkles in the laminating step in the module manufacturing process. Therefore, according to this invention, manufacture of a solar cell module becomes easy.

DESCRIPTION OF SYMBOLS 1 Solar cell module 10 Front substrate 11 Back surface protection sheet 12 Silicon battery cell 13 Silicon 15 15 'Sealing sheet

Claims (7)

A back protective sheet for a solar cell module having a single layer or a laminate, having at least one weather resistant resin sheet (A) containing an ultrahigh molecular weight polyethylene having an intrinsic viscosity of 5 dl / g or more,
The back surface protection sheet for solar cell modules whose thermal expansion in 120 degreeC (both thermal expansion in MD direction and thermal expansion of TD direction perpendicular | vertical to it) of the said weather resistant resin sheet (A) is zero or positive.   The back surface protection sheet for solar cell modules of Claim 1 whose said weather-resistant resin sheet (A) is the ultra high molecular weight polyethylene sheet formed by cutting.   Furthermore, the moisture-proof sheet | seat (B) was laminated | stacked, The back surface protection sheet for solar cell modules of Claim 1 or 2.   The back protective sheet for solar cell modules according to claim 3, wherein the moisture-proof sheet (B) is a metal aluminum sheet or a resin sheet having an inorganic film.   The back surface protection sheet for solar cell modules as described in any one of Claims 1-4 by which the surface of the said weather-resistant resin sheet (A) is corona-treated or atmospheric pressure plasma-treated. A solar cell module having a laminated back surface protection sheet,
The solar cell module whose said back surface protection sheet is a back surface protection sheet for solar cell modules of any one of Claims 1-5. A power generation facility comprising the solar cell module according to claim 6.

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